Computer systems are pervasive in the world, including everything from small handheld electronic devices, such as personal data assistants and cellular phones, to application-specific electronic devices, such as set-top boxes, digital cameras, and other consumer electronics, to medium-sized mobile systems such as notebook, sub-notebook, and tablet computers, to desktop systems, workstations, and servers.
Over the last few years, there have been many advances in semiconductor technology that have resulted in the development of improved electronic devices having integrated circuits (IC) operating at higher frequencies and supporting additional and/or enhanced features. While these advances have enabled hardware manufacturers to design and build faster and more sophisticated computer systems, they have also imposed a disadvantage in higher power consumption, especially for battery-powered computer systems.
A variety of techniques are known for reducing the power consumption in computer systems. For example, the Advanced Configuration and Power Interface (ACPI) Specification (Rev. 2.0a, Mar. 31, 2002) sets forth information about how to reduce the dynamic power consumption of portable and other computer systems. With respect to processors used in computer systems, four processor power consumption modes (C0, C1, C2, and C3) are defined in the ACPI Specification. For example, when the processor 105 is executing instructions, it is in the C0 mode. The C0 mode is a high power consumption mode. When the processor 105 is not executing instructions or idle, it may be placed in one of the low power consumption modes C1, C2 or C3. An Operating System (OS) in the computer system may dynamically transition the idle processor 105 into the appropriate low power consumption mode.
The C1 power mode is the processor power mode with the lowest latency. The C2 power mode offers improved power savings over the C1 power mode. In the C2 power mode, the processor is still able to maintain the context of the system caches. The C3 power mode offers still lower power consumption compared to the C1 and C2 power modes, but has higher exit latency than the C2 and C1 power modes. In the C3 power mode, the processor 105 may not be able to maintain coherency of the processor caches with respect to other system activities.
While the reduced power consumption modes defined by the ACPI Specification and known techniques have many advantages, there is a continuing need for ways to further reduce the power consumption of computer systems, including power consumption of individual components such as, for example, a display, a disk drive, an integrated graphics processor, etc.